During the conduct of oceanographic undersea surveillance and studies, it has been discovered that the hydrophone cable, as well as the guy cables, tend to vibrate when subjected to ocean currents. This strumming noise or sound produced by the vibrating cables are detected by the hydrophones, and the detected noise is known to interfere with the acoustic studies. In addition, it has been discovered that the strumming attracts fish, and fish have been known to attack the cable. Since it is desirable for such studies to conducted with a minimum of background noise, it should be apparent that a cable structure which does not have a proclivity to vibrate in response to ocean currents is highly desirable.
The fairing of cables in water in the sense of connecting lateral strands to cable, line or elongated structures has been used for many years and in earliest versions required attachment of the fairing material by hand operation such as connecting short pieces of line at intervals along the cable, etc.
It is known that the vibrations and hence the sound produced by vibrating undersea cables can be attenuated by providing those fairings or streamers at spaced intervals along the length of the cable. The fairings are normally fabricated of a flexible material which extends laterally of the cable so that each fairing is capable of disposing itself on the down-stream side of the cable to break-up vortices as the sea water flows across the cable. Thus the cause of cable strumming is eliminated or reduced and cable drag also tends to be reduced.
One type of faired cable which has been used comprises a series of flat relatively-narrow tapes or ribbons secured to the cable at spaced intervals along its length. Although this type of faired cable may function satisfactorily in certain situations, it has limitations. For instance, the tapes are highly flexible. As a result, they can wrap completely around the cable in response to changes in the direction of ocean currents. Needless to say, such wrapping is undesirable since it prevents the fairings from functioning properly. The tapes also have a proclivity for tearing and becoming disconnected from the cable during deployment and recovery. Furthermore, such a faired cable is expensive to manufacture.
As the technology of making rope and or cable developed layers including the outer layers were often produced by a category of apparatus known as a braiding machine which apparatus comprises a frame or base plate upon which is mounted a platen having a pair of complimentary sinusoidal grooves constituting a pair of endless sinusoidal paths disposed about a common axis. Supported in the grooves are a plurality of foot members each of which have a depending element adapted to be engaged by lugs, carried by gears or other suitable driving means disposed below the platen. Each foot member releasably supports a bobbin carrier which in turn supports a bobbin in position to feed thread therefrom through suitable thread guides and thread tensioning means. The details of the construction of the foot members, the mechanism for driving them and the bobbin carriers are no part of the present invention except that equivalent functioning elements are necessary to perform the methods disclosed herein as part of the present invention. For details of this mechanism and the general technology of braiding machines of the general type useful to practice braiding a jacket on a cable or core, reference is made to U.S. Pat. No. 2,388,693, issued Nov. 13, 1945, U.S. Pat. No. 2,354,212, issued July 25, 1944, U.S. Pat. No. 2,407,929, issued Sept. 17, 1946 and U.S. Pat. No. 2,494,389, issued Jan. 10, 1950. When all the plural bobbin carriers are disposed for movement along the sinusoidal paths of the machine the threads supported thereby are interwoven into the desired braid around the rope or core being passed upwardly along the common axis above the plurality of bobbins in the two sinusoidal paths. The bobbins in one sinusoidal path move in one direction and the bobbins in the other sinusoidal path move in the other direction. Each bobbin is providing a thread or a plurality of threads to the braid as the plurality of bobbins move around the common axis (and core material if present) to form a tubular braid material of the desired diameter determined in many applications by the size of the core material, if present. The apparatus described above is standard and in many braiding machines and a further description of one apparatus that works this way is shown in U.S. Pat. No. 2,388,693, etc. The number of bobbins can vary depending upon the application when the above described apparatus is operated to provide a braided tube or jacket tightly around the core of a cable or line (carrying electrical information) which needs the fairing material for the reasons stated above.
One way to provide fairing and avoid cable strumming have been to use polyester yarns or fibers for the final braided surface of the electrical cable because such polyester yarn or fibers have been selected because when they are brushed they provide a nap or moss effect on the cable which improves vortex shedding thus reduces strumming in low current velocities. In U.S. Pat. No. 4,084,065 dated Apr. 11, 1978, it is stated that this technique for reducing strumming is particularly suitable for acoustic sensor array applications. That technique does not provide a flexible solution to the problem because the fairing is limited to that which can be obtained from the lateral yarn or fibers which are generated by brushing the braided jacket.
In other prior art, U.S. Pat. No. 3,975,980 dated Aug. 24, 1976, the fairings are provided by a resilient fairing yarn which is fed toward the core and which is manipulated by a needle during braiding of the jacket to cause each fairing to have a base portion anchored between the jacket and the resilient layer of the core and streamer portions extending outwardly from the base portion. The needle is mounted for reciprocation parallel to the moving core upstream of the braider, and the fairing yarn passes through the eye of the needle and a first length is displaced through the path of movement of the braid yarns into engagement with a gripping assembly located downstream of the braid yarns. The gripping assembly holds the first length of fairing yarn so that as the needle retracts, another length of braid yarn is pulled through the. needle-eye. Continued operation of the braider causes the jacket to be applied around the portion of the fairing yarn engaged with the core, thereby forming the base portion for the next fairing. A control system is disclosed for synchronizing movement of the needle with the displacement of the rope and for adjusting of the spacing between the fairings. This technique works to provide fairing article whether or not there is a separately formed core. This technique does provide fairing yarn extending from the braided surface however, in some instances the strength of the fairing yarn or fairing material as separate pieces is subject to being pulled out by forces being applied to it, in other words the fair yarn or material is not integral with the material forming the braided jacket.
Still another U.S. Pat. No. 4,030,401, dated June 21, 1977, covers the product produced by the method of U.S. Pat. No. 3,975,980 herein.
Other prior art is described in U.S. Pat. No. 4,311,079 dated Jan. 19, 1982. Therein the faired article is manufactured by guiding a length of faring yarn into proximity with the upstream side of the ring of a braider, entraining the fairing yarn in an air stream directed across the path of movement of the braid yarns inside the braider ring, and causing the fairing yarn entrained therein to pass through the path of movement of the braid yarns as they advance around the braider ring, thereby enabling the braid yarns to form the fairing yarn into loops as the braid yarns form the jacket around the core. The apparatus for practicing this method is also described.
The problem with the prior art from the present inventor's point view is that the fairing material that is the material of like kind or similar kind that is associated with cables, ropes, lines and other elongated strength members requiring lateral fairing members in a fluid or water is that these members are not made an integral part of the core or the braided jacket. On reviewing the inherent problem of the prior art, the inventor felt such members could be made in an integral part of the braided jacket and the manufacture of the same would be simplified and the likelihood of the fairing material tearing or wearing away from the cable, rope line or elongated strength member would be decreased.